Pressure sensor cap having flow path with dimension variation

Abstract

Pressure sensors that may be used in flowrate monitoring or measuring systems, where the pressure sensors may enable simple, low-cost designs that are readily implemented. One example may provide a pressure sensor having a built-in flow path with a dimensional variation. Pressures of a fluid on each side of the dimensional variation may be compared to each other. The measured differential pressure may then be converted to a flowrate through the flow path.

What is claimed is: 
     
       1. A pressure sensor comprising:
 a package comprising:
 a central cavity; 
 a first passage from a top side of the package to the central cavity and forming a first opening in the central cavity; and 
 a second passage from the top side of the package to the central cavity; 
 
 a pressure sensor chip fixed to a top surface of the central cavity and over the first opening in the central cavity; and 
 a cap fixed to the top surface of the package, the cap comprising:
 a flow path forming a first opening in the cap and a second opening in the cap; 
 a first shunt passage from the flow path to a bottom side of the cap, where the first shunt passage is aligned with the first passage in the package; 
 a second shunt passage from the flow path to the bottom side the cap, where the second shunt passage is aligned with the second passage in the package; and 
 a dimensional variation in the flow path between the first shunt passage and the second shunt passage. 
 
 
     
     
       2. The pressure sensor of  claim 1  wherein the cap further comprises a first nozzle for the first opening in the cap and a second nozzle for the second opening in the cap. 
     
     
       3. The pressure sensor of  claim 2  wherein the first nozzle and the second nozzle are formed to mate with pliable tubing. 
     
     
       4. The pressure sensor of  claim 2  further comprising a signal conditioning circuit. 
     
     
       5. The pressure sensor of  claim 4  wherein the signal conditioning circuit is coupled to receive signals from the pressure sensor chip. 
     
     
       6. The pressure sensor of  claim 5  wherein the pressure sensor chip is an integrated circuit. 
     
     
       7. The pressure sensor of  claim 1  wherein the bottom side of the cap is glued to the top side of the package. 
     
     
       8. The pressure sensor of  claim 1  wherein the dimensional variation is a narrowing of the flow path. 
     
     
       9. The pressure sensor of  claim 1  wherein the dimensional variation is a venturi in the flow path. 
     
     
       10. A cap for a pressure sensor, the cap comprising:
 a flow path forming a first opening in the cap and a second opening in the cap; 
 a first shunt passage from the flow path to a bottom side of the cap, where the first shunt passage is aligned with a first passage in a package; 
 a second shunt passage from the flow path to the bottom side the cap, where the second shunt passage is aligned with a second passage in the package; and 
 a dimensional variation in the flow path between the first shunt passage and the second shunt passage. 
 
     
     
       11. The cap of  claim 10  wherein the cap further comprises a first nozzle for the first opening in the cap and a second nozzle for the second opening in the cap. 
     
     
       12. The cap of  claim 11  wherein the first nozzle and the second nozzle are formed to mate with pliable tubing. 
     
     
       13. The cap of  claim 10  wherein the dimensional variation is a narrowing of the flow path. 
     
     
       14. The cap of  claim 10  wherein the dimensional variation is a venturi in the flow path. 
     
     
       15. The cap of  claim 10  wherein the dimensional variation is formed by an obstruction in the flow path. 
     
     
       16. A pressure sensor comprising:
 a package comprising:
 a first cavity; 
 a second cavity; 
 a wall separating the first cavity from the second cavity; 
 a first passage from a top side of the package to the first cavity and forming a first opening in the first cavity; and 
 a second passage from the top side of the package to the second cavity and forming a first opening in the second cavity; 
 a first pressure sensor chip in the first cavity; 
 a second pressure sensor chip in the second cavity; and 
 
 a cap fixed to a top surface of the package, the cap comprising:
 a flow path forming a first opening in the cap and a second opening in the cap; 
 a first shunt passage from the flow path to a bottom side of the cap, where the first shunt passage is aligned with the first passage in the package; 
 a second shunt passage from the flow path to the bottom side the cap, where the second shunt passage is aligned with the second passage in the package; and 
 a dimensional variation in the flow path between the first shunt passage and the second shunt passage. 
 
 
     
     
       17. The pressure sensor of  claim 16  further comprising a signal conditioning circuit. 
     
     
       18. The pressure sensor of  claim 17  wherein the signal conditioning circuit is coupled to receive signals from the first pressure sensor chip. 
     
     
       19. The pressure sensor of  claim 16  wherein the dimensional variation is a narrowing of the flow path. 
     
     
       20. The pressure sensor of  claim 16  wherein the dimensional variation is a venturi in the flow path.